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Method for Distinguishing Metal Film Resistance from Carbon Film Resistance

Writer:Microhm Page View:Date:2018-11-27
Color ring resistors are produced using different materials, and their functions and applications are different, but they are all labeled with the same color ring recognition method. In the absence of a resistor manufacturer's instructions, how to correctly identify the type of resistance is very difficult for line engineers and maintenance personnel. Today we will talk about the method of distinguishing the carbon film resistance from the metal film resistance in the color ring resistance.


First of all, we need to understand what is a metal film resistor. In fact, this resistor is made of nickel-chromium or similar alloy vacuum plating technology. It is coated on the surface of the white porcelain rod, and the resistance value is cut by cutting to achieve the final required precision resistance. The manufacturer adds a layer of color ring to the outer layer to identify such metal film resistors. Secondly, we learned that the carbon film resistance is the carbon which separates the organic compound from the high-temperature vacuum, adheres to the carbon film body on the surface of the ceramic rod, and is cut and adjusted by appropriate joints, and is coated with epoxy on the surface to protect it. The resistance is marked by the color ring.


From the above, these two types of color ring resistors are very different from the production industry, so their characteristics are also very different. Metal film resistors have precise resistance and small tolerance range, and carbon film resistors are widely used in many electronic, electrical, and information products because of their low cost.


At present, the most common method for distinguishing carbon film resistance from metal film resistance for circuit engineering is to test the resistance value. Since the temperature coefficient of the metal film resistance is much smaller than the carbon film resistance, the engineer uses a multimeter to measure the resistance of the resistor, and then heats it. The electric ferrochrome is close to the resistor, and if the resistance value changes greatly, it is a carbon film resistor, and vice versa is a metal film resistor. Another method is to destroy the resistor for identification. This method is used as a last resort. Engineers usually use a blade to scrape off the protective paint. The exposed film is black with carbon film resistance; The brighter white film is a metal film resistor.

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